Weathering: physical, chemical, and biological

Water freezes in cracks and expands to break rocks. For exams remember that repeated temperature change is key.

Weathering is stronger at joint corners and edges so rounded blocks form. In exams treat joint pattern as the main clue.

Direct answer: C, carbonation and solution. Karst forms where limestone is dissolved by water. Rainwater absorbs carbon dioxide from air and soil, forming weak carbonic acid. This acidic water enters cracks and reacts with calcium carbonate in limestone; the mineral dissolves and is carried away. Over time this makes caves, sinkholes and underground channels. A, hydration, means water joining a mineral and is not the main karst process. B, oxidation, mainly affects minerals such as iron. C is correct because carbonated water causes limestone solution. D, thermal expansion, is physical weathering caused by heating and cooling, not the characteristic chemical basis of karst. Memory cue: karst means limestone plus carbonated water and solution.

Evaporation in dry regions enlarges salt crystals and creates pressure. For exams remember aridity with capillary water.

Heat and water increase the rate of chemical reactions. In exams connect hot humid regions with chemical weathering.

Direct answer: B, iron-bearing minerals form oxides and produce red or brown colour. Oxidation is a chemical reaction in which oxygen combines with a substance. When oxygen and moisture act on iron minerals, iron oxides or hydroxides form, much like rust on iron. These products commonly colour rocks reddish, brownish or yellowish and may weaken them. A is wrong because weathering does not turn iron minerals immediately into glass. B is correct because it states both the chemical change and the usual colour effect. C is wrong: oxidation is not vaporisation, and ordinary weathering does not make minerals simply become vapour. D is wrong because oxidation changes minerals and often changes colour; they do not remain completely stable. Exam cue: iron plus oxygen and water suggests rust, red-brown colour and chemical weathering.

The direct answer is C: physical weathering breaks rock down at its original place, whereas erosion removes and usually carries the loosened material away. Weathering is the breakdown of rock; erosion is the removal and movement of soil, rock fragments, or sediment by water, wind, ice, or gravity. Step by step: first a rock may crack because of heating, cooling, frost, or root growth; then water, wind, ice, or gravity may carry the pieces elsewhere. Option A is wrong because physical weathering usually changes size and shape, not mineral composition; chemical weathering changes composition. Option B reverses the meaning because erosion involves removal and transport, not only breaking in place. Option C correctly separates breakdown from removal. Option D is wrong because the two processes are related but not identical. Memory cue: weathering stays, erosion goes.

Hydrolysis can alter silicate minerals into clay like products. For exams remember feldspar changing into clay.

Roots exert mechanical pressure as they grow and break rock. For exams see it as biological with physical effect.

Direct answer: B, unloading and exfoliation. Granite deep underground is pressed by thick overlying rock. When erosion removes that cover, pressure on the granite decreases. The rock expands slightly, and cracks develop roughly parallel to its outer surface. Thin curved sheets can then separate or peel away; this is exfoliation, also called sheeting. A, oxidation, is a chemical reaction involving oxygen and does not explain pressure release. B is correct because it gives both the cause, unloading, and the resulting peeling, exfoliation. C, solution, is dissolution by water and is especially important in soluble rocks such as limestone. D, alluvial deposition, is the laying down of river sediment, not a granite-weathering process. Memory cue: removed load causes release, expansion and sheets peeling.

Regolith is the loose layer of weathered material above bedrock. For exams treat it as a base for soil formation.

Permeability allows water and air to reach minerals. In exams treat cracks and pores as reaction pathways.

Temperature change can split jointed rocks into blocks. For exams use day night temperature range as a clue.

Answer: C, hydration. In hydration, water is absorbed or chemically added to certain minerals. This can increase their volume, alter their structure, and make the surrounding rock weaker. The process is therefore a form of chemical weathering rather than merely the physical presence of water. A, carbonation, involves the action of carbonic acid, commonly formed when carbon dioxide dissolves in water. B, reduction, involves a chemical change associated with the removal of oxygen or gain of electrons and is not the defining process here. D, salinisation concerns the accumulation of salts and is not the mineral-water swelling process described. Memory cue: hydration contains “hydrate,” linking it with water absorption.

Lichens release biochemical substances that alter rock surfaces. For exams remember the chemical role of organisms.

Dark surfaces absorb more heat and increase expansion contraction. For exams remember the link between colour and thermal behaviour.

Low temperature slows chemical reactions but ice action breaks rocks. In exams link cold mountains with frost weathering.

Direct answer: Option D, cracks increase entry zones for water, air, and roots. Joints and cracks divide a rock surface and expose more edges. They let water, oxygen, carbon dioxide, and plant roots penetrate into the rock. These agents carry out chemical reactions, physical pressure, and biological action, so weathering becomes faster and deeper. Option A is wrong because cracks do not make rock completely waterproof. Option B is wrong because cracks do not block all sunlight and sunlight is not the main explanation. Option C is wrong because preventing sediment movement is unrelated to the cause of weathering. Option D correctly combines the important pathways and increased exposed area. Cue: more cracks mean more entrances for weathering.

In carbonation mildly acidic water helps dissolve minerals. In exams especially connect it with limestone.

Different minerals expand and contract at different rates so grains may separate. In exams use coarse texture as the clue.

Weathering prepares the mineral base of soil. For exams remember it as an initial stage of soil formation.

Temperature and water availability control physical and chemical weathering. In exams treat climate as a major control.

Reduction processes can act where oxygen is deficient. For exams connect waterlogging with reduction.

More surface allows greater action of water air and temperature. In exams remember that small particles weather faster.

The direct answer is B: solution is most visible in soluble minerals such as rock salt and gypsum. Solution is a chemical weathering process in which water dissolves a mineral and carries it in dissolved form. The reasoning is simple: water contacts a soluble substance; the substance enters the water; the dissolved material may later be transported or deposited elsewhere. Rock salt is especially soluble, and gypsum is also more soluble than many common silicate rocks. Option A is wrong because quartz and hard basalt are not the best examples of direct solution; quartz is relatively resistant. Option B is correct because it gives standard soluble minerals. Option C is wrong because dry ash is not a general example of mineral solution. Option D is wrong because fresh lava is a rock material, not the defining answer for solution. Exam cue: salt plus water means solution.